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Full text of "Circuits"

Introduction to Electronics: The Relay 



Make] Projects 

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build, hack, tweak, share, discover,- 



Introduction to Electronics: The 



Relay 

Written By: KRA5H 



TOOLS: 



PARTS: 



Snap Circuits Extreme 750 set (1) 
available at your local RadioShack store 



Battery Holder (2-AA) # 6SC B1 (1) 
Base Grid (11" x IT) # 6SC BG (1) 
Press Switch #6SCS2(1) 
RedLED#6SCD1 (1) 
Relay #6SC S3 (1) 
Conductor with 2-snaps # 6SC 02 (3) 
Conductor with 3-snaps # 6SC 03 (1) 
Conductor with 4-snaps # 6SC 04 (1) 



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Page 1 of 8 



Introduction to Electronics: The Relay 



Step 1 — Introduction to Electronics: The Relay 




• What's a relay? You've probably 
seen a relay race where one runner 
hands off a baton to another 
runner. Similarly, an electronic 
relay hands off control from one 
circuit to another. 



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Page 2 of 8 



Introduction to Electronics: 


: The Relay 




Step 2 



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Introduction to Electronics: The Relay 



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Figure 1: Relay off 



Figure 2: Relay on 



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• A relay is a very simple device 
consisting of an electromagnet, an 
armature (a switch that closes 
when attracted by the 
electromagnet), and a spring that is 
connected to the armature. You 
can see in the diagrams (Source: 
How Stuff Works) how the relay 
works. 

• In Figure 1 of the diagram, there 
are two circuits. The first circuit is 
a battery (3 volts), a switch and an 
electromagnet. The second circuit 
is a battery (6 volts), a light bulb 
and the relay's armature. While the 
switch to the electromagnet is off, 
no current can flow from the 3 volt 
battery through the electromagnet. 
So, the armature-switch is off and 
no current can flow from the 6 volt 
battery to power the lamp in the 
second circuit. 

• In Figure 2 the switch to the 
electromagnet circuit is switched 
on. When current from the 3 volt 
battery flows through the 
electromagnet, the electromagnet 
creates a magnetic field that 
attracts the armature to close the 
circuit to the lamp. Now current 
can flow from the 6 volt battery to 
the lamp, and the lamp lights up. 

• If you look closely at Figure 2, 
you'll notice that while the 
armature-switch is closed allowing 
the current in the lamp circuit to 

Page 4 of 8 



Introduction to Electronics: The Relay 



flow from the 6 volt battery to the 
lamp, it does not come into contact 
with the electromagnet. 

This means that the 6 volts from 
the lamp circuit cannot flow into the 
electromagnet circuit. Thus, the 3 
volts in the electromagnet circuit 
and the 6 volts in the lamp circuit 
remain separate. 



Step 3 




• This is the electronic schematic 
diagram of a relay. The curly line 
represents the electromagnetic coil 
and the vertical lines represent the 
metal core the coil is wrapped 
around. The switch at the top of the 
diagram represents the armature. 



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Page 5 of 8 



Introduction to Electronics 


The Relay 




Step 4 




• This is the electronic schematic of 
the circuits from figures 1 and 2 
above. 



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Page 6 of 8 



Introduction to Electronics: The Relay 



Step 5 





• Build the circuit demonstrated in the photographs. 

• When you press the Press Switch (S1) you will hear the relay click as current passes from 
the 3 volt battery block (B1) through the electromagnet. The electromagnet creates a 
magnetic field that attracts the metal armature. 

• When you release the Press Switch you will hear the relay click again since the current 
has been cut from the electromagnet. This causes the electromagnetic field to collapse so 
the armature is no longer attracted by the electromagnet and the spring attached to the 
armature returns the armature to its rest position. 

• Often when using electronic relays in circuits it is recommended that you insert a flyback 
diode to protect sensitive electronics. The magnetic coil in the relay stores electricity like 
a capacitor and when the voltage is cut from the coil the current can flow back into the 
circuit in a way that is undesirable. 

• I've included the red LED to demonstrate this phenomenon and you can review this video 
to watch the LED flash when I release the Press Switch (S2). 



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Page 7 of 8 



Introduction to Electronics 


The Relay 




Step 6 




• The following are a couple of 
videos that demonstrate the use of 
the relay in simple circuits: 

• This first video is a very simple 
circuit that launches a flying 
disc. 

• The second video demonstrates 
using the relay in a laser tripwire 
circuit to sound an alarm. 

• For a complete step-by-step build 
of the laser tripwire and alarm 
circuits, please visit my guide: 
Laser Tripwire and Alarm Using 
Snap Circuits 



Relay diagram source: http://electronics.howstuffworks.com/rel. 



This document was last generated on 201 2-1 0-30 07:1 8:40 PM. 



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Page 8 of 8